1. Field of the Invention
The present invention relates to a zircon refractory material that can be used to make a forming vessel (isopipe) that has an improved creep resistance property and is used in a glass manufacturing system to manufacture a glass sheet.
2. Description of Related Art
Corning Inc. has developed a process known as the fusion process (e.g., downdraw process) to form high quality thin glass sheets that can be used in a variety of devices like flat panel displays. The fusion process is the preferred technique for producing glass sheets used in flat panel displays because this process produces glass sheets whose surfaces have superior flatness and smoothness compared to glass sheets produced by other methods. The fusion process is described in U.S. Pat. Nos. 3,338,696 and 3,682,609, the contents of which are incorporated herein by reference.
The fusion process makes use of a specially shaped refractory block referred to as an isopipe (e.g., forming vessel) over which molten glass flows down both sides and meets at the bottom to form a single glass sheet. Although the isopipe generally works well to form a glass sheet, the isopipe is long compared to its cross section and as such can creep or sag over time due to the load and to the high temperature associated with the fusion process. When the isopipe creeps or sags too much it becomes very difficult to control the quality and thickness of the glass sheet. One way this problem can be addressed is by modifying the elements used to make the isopipe in a way that changes its physical properties in a direction that improves its resistance to creep. This is done in the present invention.